The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
For many years, calcium fructoborate (CF) has been a nutritional supplement of interest with many potential medicinal and therapeutic applications. For example, CF has been shown to be an effective antioxidant (Scorei et. al., Biological Trace Element Research 107, no. 2 (2005): 127-34), to be effective against cancer (Scorei and Popa, 2010, Anti-Cancer Agents in Medicinal Chemistry 10, no. 4 (May 1, 2010): 346-51), and to be a relatively effective modality for reducing inflammation associated with arthritis (Scorei et. al., Biological Trace Element Research 144, no. 1-3 (December 2011): 253-63). CF has also been reported for use in the treatment of skin (U.S. Pat. No. 6,080,425) and in attempts to reduce the rate of hair growth (U.S. Pat. No. 5,985,842).
All publications identified herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Synthesis of CF has been described in various sources, and one exemplary protocol can be found in U.S. Pat. No. 6,924,269 in which 0.62 g boric acid was reacted with 3.60 g fructose in 10 ml of water, with subsequent neutralization using 1 g calcium carbonate under evolution of carbon dioxide. While such process is at least conceptually simple on paper, it should be recognized that there is substantial complexity involved upon closer investigation. At the outset, commercially available fructose exists in numerous isomeric forms, having five-membered heterocyclic rings (furanose) and six-membered (pyranose) heterocyclic rings, each with their own respective stereoisomeric configuration at the anomeric carbon atom, leading to respective alpha and beta forms. Still further, fructose may also exist in open-chain forms. To complicate matters, the boric acid molecule forms diester complex bonds with two hydroxyl groups of a sugar molecule. As fructose has five hydroxyl groups (several of them in vicinal position), numerous ester products can be formed with each of the stereoisomeric form of fructose. In addition, due to the remaining hydroxyl groups in the boric acid after esterification with a first sugar molecule, further diester complex bonds can be formed with a second sugar molecule, at various positions. Exemplary stereoisomers for fructose are shown in Panel A of FIG. 1, while exemplary mono-complexes are depicted in Panel B of FIG. 1 and exemplary di-complexes are depicted in Panel C of FIG. 1. Thus, and not surprisingly, only very little information on reaction dynamics and specific product formation is known for boro-carbohydrate complexes.
For example, Edwards et al. (Journal of Food Research 3, no. 3 (May 15, 2014)) report an NMR analysis of fructoborate complexes and their distribution of stereoisomers along with stability data, and Makkee et. al. (Recueil Des Travaux Chimiques Des Pays-Bas 104, no. 9 (Sep. 2, 2010): 230-35) describe selected processes for preparation of borate complexes with saccharides in small scale under selected reaction conditions in an attempt to characterize formation of various forms. However, all or almost all of the conditions that were described as providing CF as a di-complex suffered from very low yields and/or substantial residual quantities of boric acid, which is generally undesirable. For example, Makkee et al. showed that the di-complex can be favored in reactions at high pH that utilize a large (5:1 or 10:1) fructose to boron molar ratio, however the overall yield of the CF di-complex is very poor, leaving excess quantities of free fructose which leads to a significant dilution of the desired product. On the other hand, where the fructose to boron molar ratio was reduced, free boric acid content almost exponentially increased at concurrent loss of di-complex versus mono-complex. Residual boric acid is also very undesirable due to its potential toxicity and other possible interference with biological molecules (e.g., boric acids are known to act as inhibitor to certain enzymes (e.g., urease) or Rho family of GTP-binding proteins). Such lack of specific guidance is especially disappointing as it has been speculated that the di-complex is the biologically most relevant and therefore most desirable form of CF.
Thus, while CF and other carbohydrate complexes are well known in the art, there is still a need for a process that results in a high-yield of di-complex calcium fructoborate or other boro-carbohydrate complexes. Viewed from a different perspective, it would be desirable to have a process that provides a composition comprising calcium fructoborate or other boro-carbohydrate complex with low (e.g., ≦10 wt %) residual free boric acid in the product. In the same way, it would be desirable to have a process that provides a composition with calcium fructoborate or another boro-carbohydrate complex without large amounts (e.g., ≧30 wt %) of residual fructose or other carbohydrate in the product. Finally, and viewed from yet another perspective, it would be desirable to have a process that provides a composition with a di-complex to free boric acid ratio that is at least 10:1, more preferably at least 15:1, and most preferably at least 20:1.